U.S. patent number 4,830,697 [Application Number 07/169,226] was granted by the patent office on 1989-05-16 for method and apparatus for manufacturing a magnetic recording disk.
This patent grant is currently assigned to Sony Corporation. Invention is credited to Toshio Aizawa.
United States Patent |
4,830,697 |
Aizawa |
May 16, 1989 |
Method and apparatus for manufacturing a magnetic recording
disk
Abstract
Method and apparatus for manufacturing a stretched surface
recording disk wherein a laminate is formed by superposing magnetic
sheets on upper and lower surfaces of a base with a bonding agent
being interposed between the regions to be bonded, clamping both an
outer annular portion and an inner annular portion of the resulting
laminate, displacing the clamped inner annular portion including
both magnetic sheets and the base relative to the clamped outer
annular portion in a direction perpendicular to the surface of the
base, thereby stretching the laminate and bonding the magnetic
sheets to the base while the annular portions are so displaced.
Inventors: |
Aizawa; Toshio (Miyagi,
JP) |
Assignee: |
Sony Corporation (Tokyo,
JP)
|
Family
ID: |
13311657 |
Appl.
No.: |
07/169,226 |
Filed: |
March 16, 1988 |
Foreign Application Priority Data
|
|
|
|
|
Mar 20, 1987 [JP] |
|
|
62-066294 |
|
Current U.S.
Class: |
156/163; 156/229;
264/292; 425/DIG.53; 425/383; G9B/5.295; 156/494 |
Current CPC
Class: |
G11B
5/84 (20130101); Y10S 425/053 (20130101) |
Current International
Class: |
G11B
5/84 (20060101); B32B 031/00 () |
Field of
Search: |
;156/160,163,391,494,581,229 ;360/135 ;264/106,107,291,292
;425/383,DIG.48,DIG.53 ;428/65 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ball; Michael W.
Assistant Examiner: Herb; David W.
Attorney, Agent or Firm: Hill, Van Santen, Steadman &
Simpson
Claims
I claim as my invention:
1. A method of producing a magnetic disk comprising a base having a
circular periphery interposed between two magnetic sheets, each
sheet being bonded to the base along two annular concentric
regions, said method comprising the steps of forming a lamina of
the base sandwiched between two magnetic sheets by placing a
magnetic sheet on an upper surface of the base and a second sheet
on the lower surface of the base with a bonding agent being
interposed between the sheets and base in the regions to be bonded;
clamping an inner annular portion of each of the sheets onto a
portion of the base and clamping an outer annular portion radially
outward of said inner portion and outward of the periphery of said
base, displacing the clamped inner portion including both the
magnetic sheet and said base relative to the clamped outer annular
portion in a direction perpendicular to the surface of said base so
that the two sheets between the inner clamp portion and the
periphery of the base are radially stretched; and then bonding said
magnetic sheets to said base while said annular portion is
displaced to bond the stretched sheets onto said base.
2. A method according to claim 1 wherein said bonding occurs at an
elevated temperature.
3. A method according to claim 2 wherein said temperature is
sufficient to anneal said magnetic sheets and partially relieves
stresses formed therein.
4. A method according to claim 3 wherein the stretching of the
magnetic sheets during displacing provides a tension substantially
in excess of the desired tension, and annealing reduces the tension
down to said desired tension.
5. A method according to claim 1, wherein the step of displacing
the clamped inner portion includes moving the clamped inner portion
vertically upward from the clamped outer portion and includes
holding a portion of the second magnetic sheet on the bottom
surface of the base adjacent the periphery of the base as the
sheets and base are displaced upward.
6. An apparatus for manufacturing a stretched surface recording
disk comprising a base sandwiched between two magnetic sheets which
are secured at annular portions to said base, said apparatus
comprising an anchor table having a central recess; a shift member
positioned in said central recess of said anchor table; means
engaging said shift member for vertically displacement of the
member relative to said anchor table; means coacting with said
shift member for clamping an inner annular portion of each of the
magnetic sheets and the base to be laminated to said shift member
to move therewith; means for clamping an outer annular portion of
each of the magnetic sheets at a position outside of a circular
periphery of the base so that when the shift member and the clamped
inner portion are shifted relative to the means for clamping the
outer portion, each of the sheets is stretched radially on said
base.
7. An apparatus according to claim 6, wherein the shift member has
an annular ridge for holding a magnetic sheet against the surface
of the base adjacent the periphery thereof as the shift member is
displaced relative to the means for clamping the outer annular
portions of the magnetic sheets.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is in the field of manufacturing magnetic
recording disks from a laminate of magnetic sheets on a base and
stretching the sheets prior to completing the bonding to the
base.
2. Description of the Prior Art
The prior art has provided examples of tension type magnetic disks
wherein magnetic sheets are joined under tension to upper and lower
surfaces of a relatively rigid base in such a manner that a narrow
gap is held between the magnetic recording region of each sheet and
the base. Such magnetic disks and a method of producing the same
are disclosed, for example, in European Patent Application No.
186427. The method described in this application, however, presents
a variety of problems. For example, it is not adapted for
continuous manufacture since the magnetic sheets on the two
surfaces must be tensioned by temporary holders and only a small
tension adjustment range is possible for the two magnetic sheets.
Furthermore, an annealing step is necessary to release the stress
caused in the magnetic sheets due to the tensioning operation, and
the annealing step must be performed independently of the bonding
step. Therefore, the disclosed process provides operational
difficulties and problems with respect to product quality.
Other types of stretched surface recording disks and methods for
their manufacture will be found, in general, in the following U.S.
Pat. Nos.:
4,365,257
4,464,693
4,543,619
4,573,096
4,573,097
4,581,667
4,623,570
4,625,384
4,631,609
4,670,072
SUMMARY OF THE INVENTION
The present invention provides a method for manufacturing a
magnetic recording disk in which stretched magnetic sheets are
bonded to both sides of a disk shaped base simultaneously. The
method is such that it lends itself to mass production techniques
which provides improved productivity.
In the present invention, a magnetic disk is produced by first
forming a laminate of a core or base and two magnetic sheets
superposed on the upper and lower surfaces of the base with a
bonding agent being interposed between predetermined regions of the
sheets and the base. The outer annular portion and the inner
annular portion of the laminate are clamped together and then the
clamped inner portion of the laminate is displaced relatively to
the clamped outer portion in a direction perpendicular to the
surface of the base. This causes each of the two magnetic sheets to
be tensioned with the required tension. While under tension, the
bonding to the base occurs by subjecting the laminate to an
elevated temperature, whereby the two magnetic sheets are joined to
the base simultaneously with the required tension maintained. The
bonding may be accompanied by an annealing of the sheets under
tension so as to relieve some of the stress present, down to a
predetermined value.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view illustrating an initial stage in
the formation of the improved magnetic disk of the present
invention;
FIG. 2 is a view similar to FIG. 1 but showing the condition during
the tensioning stage;
FIG. 3 is a cross-sectional view of the finished magnetic disk;
and
FIG. 4 is an exploded view of the assembly shown in both FIGS. 1
and 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in FIG. 1, the present invention involves forming a
laminate by superposing magnetic sheets 2A and 2B on upper and
lower surfaces of a relatively rigid base 1 while interposing a
bonding agent between the regions which are to be mutually bonded.
The method involves clamping an inner portion and an outer portion
of the laminate and lifting the clamped inner portion of the
laminate relative to the clamped outer portion in a direction
perpendicular to the surface of the base 1 as shown in FIG. 2 while
keeping the magnetic sheets 2A and 2B in contact with the outer
portion of the base 1. Then, bonding is accomplished while the
sheets are under tension due to the displacement between the outer
and inner annular portions.
As shown in FIG. 1, the two magnetic sheets 2A and 2B are clamped
annularly in the outer portions thereof beyond the periphery of the
base 1. The inner portions of the two magnetic sheets 2A and 2B are
supported annularly and pressed fixedly against the surfaces of the
central portion of the base 1 in such a manner as to be movable
relative to the clamped outer portion in a direction perpendicular
to the surface of the base 1.
In the method of the present invention, the two magnetic sheets 2A
and 2B are simultaneously stretched outwardly, i.e., radially and
are kept taut with the required tension. By heating and hardening
the bonding agent which is typically a thermosetting resin, or the
like, interposed between the regions of the base 1 and the two
magnetic sheets 2A and 2B to be bonded, there is produced, as
illustrated in FIG. 3, a magnetic disk 3 wherein the magnetic
sheets 2A and 2B are adhered to the opposed surfaces of the base 1.
The tension on each of the magnetic sheets 2A and 2B can be
adjusted over a wide range by controlling the amount of relative
lifting of the clamped inner portion with respect to the clamped
outer portion.
Turning to the apparatus, the base 1 is shown shaped into a
circular disk with a center hole 4, and annular grooves 5A and 5B
each having a predetermined width W formed in the upper and lower
surfaces of the base 1 concentrically in at least the recording
regions of the magnetic disk 3. Annular outer reference planes 6A1,
6B1 and annular inner reference planes 6A2, 6B2 perpendicular to
the axis of the base 1 are formed at the outer edge and the inner
edge of the annular grooves 5A and 5B. One flat surface is defined
by the planes 6Al an 6A2, and another flat surface is defined by
the planes 6B1 and 6B2, respectively. Outer bevels 7A1 and 7B1 are
formed in the peripheries of the outer reference planes 6A1 and 6B1
so that the base 1 becomes gradually thinner toward the
circumference from the reference planes 6A1 and 6B1. Inner bevels
7A2 and 7B2 are formed inside the inner reference planes 6A2 and
6B2 closer to the central portion of the base 1 so that the base 1
becomes gradually thinner toward the center. If necessary, annular
grooves 8A1, 8A2 and 8B1, 8B2 for receiving excess bonding agents
may be formed in the bevels 7A1, 7A2 and 7B1, 7B2,
respectively.
The base 1 may be composed of a metal plate of aluminum or an
aluminum alloy, or the like, or may be molded out of thermosetting
or thermoplastic resin. Typically, the base 1 can be produced by
injection molding a polymer material with or without a filler mixed
therein. The polymer material may be a resin such as a polysulfone,
a polyphenylene, a polyester, or a polyetherimide. Non-magnetic
inorganic particles of glass, glass beads, calcium carbonate, or
the like may be included as a filler.
Each of the magnetic sheets 2A and 2B is composed of a non-magnetic
plastic sheet of polyethylene terephthalate film or the like with a
magnetic layer being formed thereon. The magnetic layer can be made
by coating a magnetic paint composed of magnetic particles in a
binder or a magnetic thin film of a ferromagnetic metal such as
cobalt, nickel, iron, or alloys thereof can be deposited directly
on the plastic sheet by sputtering, vacuum evaporation, ion plating
or liquid phase plating.
The magnetic sheets 2A and 2B are so positioned that the
non-magnetic plastic surfaces thereof are kept in contact with the
outer and inner reference planes 6A1 and 6A2, 6B1 and 6B2,
respectively, on the upper and lower surfaces of the base 1 and the
inner and outer portions are bonded respectively to the bevels 7A1
and 7A2, 7B1 and 7B2.
The bonding agent is applied annularly on to the regions of the
base 1 for bonding the magnetic sheets 2A and 2B thereto, i.e., on
to the bevels 7A1 and 7A2, 7B1 and 7B2 and/or on to the regions of
the magnetic sheets 2A and 2B corresponding to the bevels 7A1 and
7A2, 7B1 and 7B2. The glass transition temperature of the bonding
agent should be substantially higher than room temperature, e.g.,
more than 120.degree. C. It is desired that the bonding agent be of
the thermosetting type such as an epoxy adhesive wherein an epoxy
resin and a hardening agent are reacted upon heating. A typical
hardening agent adapted for this use is, for example, dicyandiamide
which evidences almost no reaction at room temperature or at
customary preservation temperatures, but is rendered active ween
heated up to 150.degree. C. or so and reacts with the epoxy radical
in the epoxy resin. One such epoxy bonding agent available is known
as "XNR3505" which is a product of CibaGeigy Ltd.
The joining and a jig to be used therefore will be described below.
As shown in the exploded view of FIG. 4, the jig includes a spacer
ring 9 having an inner diameter greater than the outer diameter of
the base 1 and having a thickness corresponding to the thickness t
between the reference planes 7A1 and 7B1 of the base 1 and also
between the reference planes 7A2 and 7B2.
The assembly includes an anchor table 12 having a circular shallow
recess 10 with an inner diameter greater than the outer diameter of
the spacer ring 9 and also a circular deep recess 11 formed at its
center. In the recess 11, a shaft 13 is rotatably supported along
the axis. The shaft support member 14 such as a ball bearing
provides support for the shaft. At the inner end of the shaft 13
there is disposed a screw rod 15 which is held so as to be
rotatable with the shaft 13 and has a screw thread about its
peripheral surface. In the bottom portion of the recess 11, guide
pins 16 are fixed upright about the axis of the recess 11.
In the recess 11 there is provided a shift member 17 which is
movable vertically relative to the anchor table 12 along the axis
of the recess 11. The shift member 17 has through holes 18 for the
insertion of guide pins 16 and also has, in its central portion, a
lead screw 19 engageable with the screw rod 15 so that when the
screw rod 15 is rotated together with the shaft 13, the lead screw
19 is moved up or down along the screw rod to consequently cause a
vertical motion of the shift member 17. On the top surface of the
shift member 17 there is integrally formed an inner tilt ring 20
which has in its upper end face a slope formed corresponding to the
inner bevel 7B2 on the lower surface of the base 1. In the outer
portion there is integrally formed an outer tilt ring 21 which has,
on its upper end face, a slope formed corresponding to the outer
bevel 7B1 on the lower surface of the base 1. In the central
portion of the shift member 17 there is formed a shaft 23 which has
a center lead screw 22 which is insertable into the center hole 4
of the base 1.
If necessary, an O-ring 24 may be disposed in the outer bottom
portion of the shallow recess 10. There is further provided an
inner clamp member 25 for clamping the inner portions of the
magnetic sheets 2A and 2B in cooperation with the shift member 17.
The clamp member 25 is equipped on its lower end face with an
inclined ring 251 which has a bevel corresponding to the inner
bevel 7A2 of the base 1. The clamp 25 can be formed by a columnar
body having along its central axis a clamping screw rod 26 engaged
with the center lead screw 22 of the shaft 23 on the shift member
17.
An outer clamp member 27 is provided for clamping the outer
portions of the magnetic sheets 2A and 2B jointly against the
anchor table 12. The outer clamp member 27 is shaped in the form of
a ring and has on its lower surface an annular projection 28 which
is inserted into the shallow recess 10 of the anchor table 12. The
clamp member 27 further has, at its periphery, a flange 29 butting
against the top end face of the outer portion of the anchor table
12, the flange 29 being furnished with set screws 30 which are
driven into screw holes 31 formed in the top end face of the outer
portion of the anchor table 12.
With the structure described, a magnetic sheet 2B is placed in the
shallow recess 10 of the anchor table 12 as illustrated in FIG. 1.
The magnetic layer of the magnetic sheet 2B faces the anchor table.
The sheet 2B is so formed as to have an outer shape greater in
diameter than the base 1 and corresponding to the inner shape of
the recess 10. It has, in its central portion, a center hole 32B
which is smaller in diameter than the inner tilt ring 20 and
extends through the shaft 23. The base 1 is set on the magnetic
sheet 2B with a shaft 23 of the shift member 17 inserted into the
center hole 4, and the spacer ring 9 is disposed around the base 1.
Subsequently the second magnetic sheet 2A is placed in the hollow
recess 10 of the anchor table 12 astride the base 1 and the spacer
ring 9. The non-magnetic base side of the sheet 2A faces the base
1. The sheet 2A is so formed as to have an outer shape greater in
diameter than the base 1 and corresponding to the inner shape of
the recess 10. It has, in its central portion, a center hole 32A
which is smaller in diameter than the tilt ring 251 of the inner
clamp member 25 and extends through the shaft 23 of the shift
member 17. Then the screw rod 26 of the inner clamp member 25 is
engaged with the center lead screw 22 of the shaft 23, and the
inner clamp member 25 is tightened to the state where the two
magnetic sheets 2A, 2B and the base 1 are held between the two tilt
rings 20 and 251. (In the showing of FIG. 1, the clamp member 25 is
not tightened completely and therefore sufficiently firm clamping
is not yet achieved).
When the outer clamp member 27 is tightened on the anchor table 12
by driving the set screws 30 into the screw holes 31, the outer
portions of the two magnetic sheets 2A and 2B are clamped while
being held between the bottom of the recess or the O-ring 24 and
the projection 28 of the clamp member 27.
In this state, the shaft 13 is rotated to move the shift member 17
upwardly so that, as illustrated in FIG. 2, the clamped inner
portion of the laminate of the two magnetic sheets 2A, 2B and the
base 1 interposed therebetween is lifted relative to the clamped
outer portion in a direction perpendicular to the surface of the
base 1. Since the two magnetic sheets 2A and 2B are clamped at the
inner and outer portions thereof, the two sheets are stretched
radially and are thereby rendered taut with tension existing
between the two clamped portions.
With the laminate of the base 1 and the two magnetic sheets 2A and
2B held in the anchor table by the inner clamp member 25 and the
outer clamp member 27, the whole assembly is heated in a tunnel
furnace or the like to a temperature range of 100.degree. to
180.degree. C. for a predetermined time such as a temperature of
150.degree. C. for thirty minutes. The bonding agent is hardened to
bond the magnetic sheets 2A and 2B to the bevel 7A1, 7A2, 7B1 and
7B2 of the base 1. At this stage, due to the existence of the
grooves 8A1, 8A2, 8B1 and 8B2, any surface bonding agent is
deposited into the grooves and is thereby prevented from flowing
toward and into the annular grooves 5A and 5B in the base 1. In the
same step as the heat treatment occurs for hardening the bonding
agent, it becomes possible to perform an annealing for elimination
of the stress caused in the magnetic sheets 2A and 2B as a result
of the stretching.
The tension applied in joining the magnetic sheets 2A and 2B to the
base can be adjusted by properly selecting the amount of lift of
the clamped inner portion from the clamped outer portion in the
above described jig and the thickness of the spacer ring 9. In
order to finally obtain a desired tension after annealing the
magnetic sheets 2A and 2B, the tension to be applied in the above
step is so adjusted as to be two to three times the final
tension.
When the magnetic sheets 2A and 2B are bonded to the upper and
lower surfaces of the base 1, the peripheral regions of the
magnetic sheets 2A and 2B projecting beyond the periphery of the
base are severed and removed. Then, as illustrated in FIG. 3, the
magnetic sheets 2A and 2B positioned between the upper reference
planes 6A1 and 6A2 and between the lower reference planes 6B1 and
6B2 of the base 1 can be stretched while flat with a predetermined
tension so that a gap corresponding to the depth of the grooves 5A
and 5B is maintained over the width W between the base 1 and each
of the magnetic sheets 2A and 2B on the annular grooves 5A and 5B,
whereby a desired tension type magnetic disk 3 is obtained.
It is to be understood that the aforementioned jig can be modified
into a variety of structures. As for the bonding agent, the epoxy
adhesive is convenient for handling, but other adhesives are usable
as well. The bonding agent is not limited to thermosetting
materials alone and may be composed of a radiation curable type
resin or other suitable material.
According to the present invention as described above, magnetic
sheets 2A and 2B positioned on the two surfaces of a base 1 are
clamped in both the inner and outer portions thereof, and the
clamped portions are displaced relatively from each other so that
the two magnetic sheets 2A and 2B are stretched simultaneously with
the required tension. Thus, in comparison with the conventional
process of stretching the magnetic sheets individually, the
operation can be simplified considerably to bring about a
substantial improvement. The jig used for performing the clamping
and tensioning steps can be further utilized for hardening the
bonding agent in a tunnel furnace and also for annealing the
magnetic sheets 2A and 2B to reduce the stress caused in the
stretching stage. Consequently, the process can be carried out as a
continuous operation, leading to high mass productivity. The method
also results in magnetic disks of remarkably uniform quality.
It will be evident that various modifications can be made to the
described embodiments without departing from the scope of the
present invention.
* * * * *